Fig. 6
From: Can accelerometry be used to distinguish between flight types in soaring birds?
Time series plot of altitude (m), a single magnetometry channel (gauss), relative airspeed (V) and centred smoothed surge (g). Airspeed is relatively low with little variation when circling and gaining height in a thermal updraught (light grey) compared to straight gliding flight (dark grey). Airspeed is greatest upon leaving the thermal and decreases through the inter-thermal glide (dark grey)